# Is there a convention for the ordering of phases in three-phase power in the US?

I recently moved my small machine shop to a new location. Both locations had 3-phase power, and I wired up a 3-phase air compressor in both locations.

In both locations, I used the convention of black-red-blue wiring on L1-L2-L3 bus bars in the electrical panel.

But in the new location, the motor is running backward, indicating reversal of two of the wires (or that the previous location was “incorrect”).

I can't find anything online that says L2 should lag L1 by 120°, and L3 should lag L2 by 120°, but is that the convention? Are the mains leading into my panel (new or old) mis-wired? Or did I just make a mistake somewhere?

My specific question: what is the required phase relationship between L1, L2, and L3 (if any)?

• Each country has their own colour codes, and while in theory this should work well, in practice it is so often messed up that there is a good market for rotation direction testers and adapter plugs to change rotation direction. I even have a few 32A and 63A plugs where inside the plug you can change the direction (upload.wikimedia.org/wikipedia/commons/thumb/0/0b/…) Nov 10, 2017 at 22:43
• I'm not asking about the color codes, but rather the phase relationship.
– Rick
Nov 11, 2017 at 0:09

They sell testers for this purpose starting at < $20- sometimes running in reverse can cause severe damage to machinery. I would not trust that the convention was followed even if there is one, in such a case. I also cannot recommend the cheap testers, especially on > 240VAC due to potential for arc flash and such like- a real and appropriate CAT number should be present. Something from a reputable maker might be more like$150 (the one shown above is of the former category and is sold on Amazon- meaning that they probably are required to carry enough liability insurance to cover your next of kin).

Older testers actually had a small 3-phase motor and you would observe the direction of rotation, but newer ones are generally electronic.

Directly in answer to your question, the color code is listed as "common practice" in the US and "mandatory" in Canada as follows (somewhat unofficial source here):

• I expect the colours "red, blue and yellow" - what's green? Nov 10, 2017 at 21:35
• @SolarMike Yellow, Green and Red are Chinese standard for 3-phase. Green + yellow stripe is ground. I said it was a cheap one. ;-) Nov 10, 2017 at 21:44